Lost circulation compositions and associated methods

ABSTRACT

An embodiment includes a method of servicing a well bore. The method may comprise introducing a lost circulation composition into a lost circulation zone, the lost circulation composition comprising hydraulic cement, nano-particles, amorphous silica, clay, and water. The method further may comprise allowing the lost circulation composition to set in the lost circulation zone. Another embodiment includes a lost circulation composition. The lost circulation may comprise hydraulic cement, nano-particles, amorphous silica, clay, and water.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patent application Ser. No. 12/567,782, filed Sep. 27, 2009, entitled “Cement Compositions and Methods Utilizing Nano-Clay,” which is a continuation-in-part of U.S. patent application Ser. No. 12/263,954, filed Nov. 3, 2008, entitled “Cement Compositions and Methods Utilizing Nano-Hydraulic Cement,” which is a continuation-in-part of U.S. patent application Ser. No. 11/747,002, now U.S. Pat. No. 7,559,369, filed on May 10, 2007, entitled “Well Treatment Compositions and Methods Utilizing Nano-Particles.” The entire disclosures of these applications are incorporated herein by reference.

BACKGROUND

The present invention relates to servicing a well bore and, in certain embodiments, to the introduction of compositions into a well bore to reduce the loss of fluid into the formation.

A natural resource such as oil or gas residing in a subterranean formation can be recovered by drilling a well bore into the formation. A well bore is typically drilled while circulating a drilling fluid through the well bore. Among other things, the circulating drilling fluid may lubricate the drill bit, carry drill cuttings to the surface, and balance the formation pressure exerted on the well bore. One problem associated with drilling may be the undesirable loss of drilling fluid to the formation. Such lost fluids typically may go into, for example, fractures induced by excessive mud pressures, into pre-existing open fractures, or into large openings with structural strength in the formation. This problem may be referred to as “lost circulation,” and the sections of the formation into which the drilling fluid may be lost may be referred to as “lost circulation zones.” The loss of drilling fluid into the formation is undesirable, inter alia, because of the expense associated with the drilling fluid lost into the formation, loss of time, additional casing strings and, in extreme conditions, well abandonment. In addition to drilling fluids, problems with lost circulation may also be encountered with other fluids, for example, spacer fluids, completion fluids (e.g., completion brines), fracturing fluids, and cement compositions that may be introduced into a well bore.

One method that has been developed to control lost circulation involves the placement of lost circulation materials into the lost circulation zone. Conventional lost circulation materials may include fibrous, lamellated or granular materials. The lost circulation materials may be placed into the formation, inter alia, as part of a drilling fluid or as a separate lost circulation pill in an attempt to control and/or prevent lost circulation. For a number of reasons, use of lost circulation materials may not provide a desirable level of lost circulation control in all circumstances.

Another method that has been developed to control lost circulation involves the placement of a settable composition into the well bore to seal the lost circulation zone. To be effective, the settable composition should ideally maintain a low viscosity while under shear, but, when allowed to remain static, the composition should develop gel strength quickly with the ability to thin and flow when shear is re-applied. Rapid development of compressive strength is also desired after placement into the lost circulation zone. Conventional low-density cement compositions can be used, but typically do not exhibit the properties to successfully seal the zone. Faster setting compositions that can be used include, for example, mixtures of clay and aqueous rubber latex or hydratable polymers, which can become semi-solid upon contact with the drilling fluid, sealing the lost circulation zone. Cement can be added to these systems where additional strength is desired. Drawbacks to these faster setting compositions include lack of bonding to the subterranean formation, lack of ability to thin when shear is re-applied and dependency upon mixing of two streams, which can be very difficult to control.

SUMMARY

The present invention relates to servicing a well bore and, in certain embodiments, to the introduction of compositions into a well bore to reduce the loss of fluid into the formation.

An embodiment includes a method of servicing a well bore. The method may comprise introducing a lost circulation composition into a lost circulation zone, the lost circulation composition comprising hydraulic cement, nano-particles, amorphous silica, clay, and water. The method further may comprise allowing the lost circulation composition to set in the lost circulation zone.

Another embodiment includes a method of servicing a well bore. The method may comprise introducing a lost circulation composition into a lost circulation zone. The lost circulation composition may comprise Portland cement in an amount of about 10% to about 20% by weight of the lost circulation composition, nano-silica in an amount of about 0.5% to about 4% by weight of the lost circulation composition, the nano-silica having a particle size of about 1 nanometer to about 100 nanometers, amorphous silica in an amount of about 5% to about 10% by weight of the lost circulation composition, synthetic clay in an amount of about 0.5% to about 2% by weight of the lost circulation composition, and water in an amount of about 60% to about 75% by weight of the lost circulation composition. The method further may comprise allowing the lost circulation composition to set in the lost circulation zone.

Yet another embodiment includes a lost circulation composition. The lost circulation may comprise hydraulic cement, nano-particles, amorphous silica, clay, and water.

The features and advantages of the present invention will be apparent to those skilled in the art upon reading the following description of specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings illustrate certain aspects of some of the embodiments of the present invention, and should not be used to limit or define the invention.

FIG. 1 is a graph of a thickening time test.

FIGS. 2-3 are graphs of compressive strength tests.

FIG. 4 is a graph of a thickening time test.

FIG. 5 is a graph of a compressive strength test.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention relates to servicing a well bore and, in certain embodiments, to the introduction of compositions into a well bore to reduce the loss of fluid into the formation. There may be several potential advantages to the methods and compositions of the present invention, only some of which may be alluded to herein. One of the many potential advantages of the methods and compositions of the present invention is that the lost circulation compositions should develop sufficient static gel strength in a short time frame to be effective at lost circulation control. Another potential advantage is that the lost circulation compositions should be shear sensitive so that the compositions should remain pumpable for sufficient time for placement, but when static, the compositions should develop gel strength in a short period of time followed by rapid compressive strength development. The lost circulation composition should develop gel strength when shear is removed, but should thin when the shear is re-applied. The lost circulation composition properties described above should not be overly dependent on the temperature of the well, for example.

An embodiment of the lost circulation compositions of the present invention may comprise hydraulic cement, nano-particles, amorphous silica, clay, and water. Those of ordinary skill in the art will appreciate that embodiments of the lost circulation compositions generally should have a density suitable for a particular application. By way of example, the lost circulation compositions may have a density in the range of from about 6 pounds per gallon (“ppg”) to about 14 ppg. In certain embodiments, the lost circulation compositions may have a density in the range of from about 8 ppg to about 12 ppg and, alternatively, about 9 ppg to about 11 ppg. Embodiments of the lost circulation compositions may be foamed or unfoamed or may comprise other means to reduce their densities, such as hollow microspheres, low-density elastic beads, or other density-reducing additives known in the art. Those of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate density for a particular application.

Embodiments of the lost circulation compositions of the present invention may comprise hydraulic cement. The hydraulic cement should, for example, provide bonding of the lost circulation composition to the formation in addition to compressive strength. Any of a variety of hydraulic cements suitable for use in subterranean operations may be used in accordance with embodiments of the present invention. Suitable examples include hydraulic cements that comprise calcium, aluminum, silicon, oxygen and/or sulfur, which set and harden by reaction with water. Such hydraulic cements, include, but are not limited to, Portland cements, pozzolana cements, gypsum cements, high-alumina-content cements, slag cements, and combinations thereof. In certain embodiments, the hydraulic cement may comprise a Portland cement. Portland cements that may be suited for use in embodiments of the present invention may be classified as Class A, C, H and G cements according to American Petroleum Institute, API Specification for Materials and Testing for Well Cements, API Specification 10, Fifth Ed., Jul. 1, 1990. In addition, in some embodiments, hydraulic cements suitable for use in the present invention may be classified as ASTM Type I, II, or III.

The hydraulic cement may be present in the lost circulation composition in an amount, for example, of about 0.1% to about 25% by weight of the composition. In some embodiments, the hydraulic cement may be present in amount of about 10% to about 20% by weight of the composition. In some embodiments, the hydraulic cement may be present in amount of about 13% to about 20% by weight of the composition. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the hydraulic cement to include for a chosen application.

Embodiments of the lost circulation compositions further may comprise nano-particles. Examples of suitable nano-particles include nano-silica, nano-alumina, nano-zinc oxide, nano-boron, nano-iron oxide, nano-calcium carbonate, nano-clays, and combinations thereof. In an embodiment, the nano-particles comprise nano-silica. The nano-particles may be present in the lost circulation compositions in an amount of from about 0.1% to about 10% by weight of the composition, for example. In an embodiment, the nano-particles may be present in the lost circulation composition in an amount of about 0.5% to about 5% by weight of the composition. In an embodiment, the nano-particles may be present in the lost circulation composition in an amount of about 1% to about 5% by weight of the composition. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the nano-particles to include for a chosen application.

In an embodiment, the nano-silica may include colloidal nano-silica. An example of a suitable colloidal nano-silica is Cemsyn LP, which is available from by Bee Chems, India. The nano-silica may be present in the lost circulation composition in an amount of about 0.1% to about 5% by weight of the composition, for example. In an embodiment, the nano-silica may be present in the lost circulation composition in an amount of about 0.5% to about 4% by weight of composition. In an embodiment, the nano-silica may be present in the lost circulation composition in an amount of about 1% to about 3% by weight of composition. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the nano-silica to include for a chosen application. While the nano-particles may include nano-silica, it should be understood that the lost circulation composition may comprise less than about 25% silica by weight of the hydraulic cement on a dry basis (“bwoc”), in accordance with embodiments of the present invention. Furthermore, it should be understood that the nano-silica may be essentially free of silica fume, in accordance with embodiments of the present invention.

Generally, the term “nano-particle” is defined as having a particle size of less than or equal to about 100 nanometers (“nm”). As used herein, “particle size” refers to volume surface mean diameter (“D_(S)”) which is related to the specific surface area. Volume surface mean diameter may be defined by the following formula: D_(S)=6/(Φ_(S)A_(w)ρ_(p)) where Φ_(S)=sphericity; A_(w)=Specific surface area and ρ_(p)=Particle density. It should be understood that the particle size of the nano-particle may vary based on the measurement technique, sample preparation, and sample conditions (e.g., temperature, concentration, etc.). One technique for measuring particle size of the nano-particle at room temperature (approx. 80° F.) includes dispersing the nano-particle in a suitable solvent (such as chloroform, dichloroethane, acetone, methanol, ethanol, water, etc.) by sonification and proper dilution. A dispersing agent may be used to deagglomerate the nano-particles, if needed. The diluted, dispersed solution may then be placed on a carbon-coated copper grid with 300 mesh size by using a micropipette. It may then be dried and examined by Transmission electron microscopy (TEM). The particle size distribution may be obtained with high accuracy using an appropriate computation technique. By way of example, TEM image processing may use image-processing software such as Image-Pro® Plus software from Media Cybernetics to determine the particle size. Another example technique involves use of calibrated drawing tools in Digital Micrograph software followed by statistical analysis of the data with Kaleida-Graph software to determine the particle size.

In certain embodiments, the nano-particles may have a particle size in the range of from about 1 nm to about 100 nm (about 1×10⁻⁹ m to about 100×10⁻⁹ m). In certain exemplary embodiments, the nano-particle may have a particle size of less than or equal to about 50 nm. For example, the nano-particles may have a particle size in the range of from about 5 nm to about 50 nm. In further exemplary embodiments, the nano-particles may have a particle size of less than or equal to about 30 nm. For example, the nano-particles may have a particle size in the range of from about 5 nm to about 30 nm. In certain embodiments, the nano-particles may comprise colloidal silica having a particle size in the range of from about 5 nm to about 20 nm. However, it should be noted that the particular nano-particle chosen may be used in combination with differently sized particles of the same material, in accordance with present embodiments. For example, where nano-silica is used, silica with particle sizes greater than 100 nm may be included in a cement composition in accordance with present embodiments.

It is now recognized that the nano-particles utilized in combination with the hydraulic cement in the present embodiments, may have an impact on certain characteristics of the lost circulation compositions that should enable the compositions to effectively control lost circulation. Among other things, inclusion of the nano-particles should provide lost circulations compositions that develop rapid static gel strength while remaining pumpable for long periods of time when under shear, thus allowing sufficient time for placement, in accordance with embodiments of the present invention. For example, inclusion of nano-silica and synthetic clay in a lost circulation composition comprising hydraulic cement and amorphous silica provided a composition characterized by rapid static gel strength followed by compressive strength development. However, even though the composition developed rapid static gel strength, the composition was further characterized by thickening times while under shear that should allow placement into a lost circulation zone.

Embodiments of the lost circulation compositions further may comprise amorphous silica. Among other things, the amorphous silica may impart viscosity to the lost circulation composition. In general, amorphous silica is a high surface area, non-crystalline form of silica. An example of a suitable amorphous silica is Silicalite™ cement additive, available from Halliburton Energy Services, Inc. The amorphous silica may be present in the lost circulation compositions, for example, in an amount of about 0.1% to about 15% by weight of the composition, for example. In an embodiment, the amorphous silica may be present in an amount of about 1% to about 15% by weight of the composition. In an embodiment, the amorphous silica may be present in an amount of about 5% to about 10% by weight of the composition. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the amorphous silica to include for a chosen application.

Embodiments of the lost circulation compositions further may comprise a clay. In an embodiment, the clay may include a colloidal clay, nano clay, or a combination thereof which, for example, works synergistically with the other components in the lost circulation composition to achieve the desired properties. In an embodiment, the clay may comprise a synthetic clay. In an embodiment, the clay may comprise a synthetic nano-clay. Synthetic clays can be developed having properties similar to or better than naturally occurring clays, for example. Most clay minerals found naturally are in an unpure state with purification being potentially difficult and expensive. In addition, the natural supply of certain clay minerals may be limited. An example of a suitable synthetic clay is Themavis™ additive, available from Halliburton Energy Services, Inc. The clay may be present in the lost circulation composition in an amount of about 0.1% to about 2% by weight of the composition, for example. In an embodiment, the clay may be present in an amount of about 0.5% to about 2% by weight of the composition. In an embodiment, the clay may be present in an amount of about 0.5% to about 1% by weight of the composition. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the clay to include for a chosen application.

The water used in embodiments of the lost circulation compositions of the present invention may be freshwater or saltwater (e.g., water containing one or more salts dissolved therein, seawater, brines, saturated saltwater, etc.). In general, the water may be present in an amount sufficient to form a pumpable slurry. By way of example, the water may be present in the lost circulation compositions in an amount in the range of from about 50% to about 80% by weight of the lost circulation composition. In an embodiment, the water may be present in an amount of about 60% to about 75% by weight of the composition.

Embodiments of the lost circulation compositions may further comprise an acid-soluble filler. The acid-soluble filler may be used, for example, to provide an acid-soluble component so that the lost circulation compositions can be dissolved and removed. This may be desirable, for example, if the lost circulation composition is used in a producing zone. Examples of suitable acid-soluble fillers include dolomite, magnesium carbonate, calcium carbonate, and zinc carbonate. In an embodiment, the acid-soluble filler may include sub micron size filler having particle size in the range of 100 nm to 1 micron and, for example, between 200 nm to 800 nm. For example, sub micron-calcium carbonate may be used in accordance with embodiments of the present invention. In one embodiment, the calcium carbonate may have a particle size greater than 1 micron. Where used, the acid-soluble filler may present in the lost circulation compositions in an amount of from about 0.1% to about 300% by weight of the hydraulic cement. In an embodiment, the acid-soluble filler is present in an amount of from about 15% to about 50% by weight of the hydraulic cement. One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of the acid-soluble filler to include for a chosen application.

Other additives suitable for use in subterranean cementing operations also may be added to embodiments of the lost circulation compositions, in accordance with embodiments of the present invention. Examples of such additives include, but are not limited to, strength-retrogression additives, set accelerators, set retarders, weighting agents, lightweight additives, gas-generating additives, mechanical property enhancing additives, lost-circulation materials, filtration-control additives, dispersants, a fluid loss control additive, defoaming agents, foaming agents, thixotropic additives, and combinations thereof. An example of a suitable fluid loss control additive is HALAD® 344 fluid loss additive, available from Halliburton Energy Services, Inc. Specific examples of these, and other, additives include crystalline silica, fumed silica, salts, fibers, hydratable clays, calcined shale, vitrified shale, microspheres, fly ash, slag, diatomaceous earth, metakaolin, rice husk ash, natural pozzolan, zeolite, cement kiln dust, lime, elastomers, resins, latex, combinations thereof, and the like. By way of example, retarders may be included for high temperatures and heavy weight additives may be incorporated for high density composition. A person having ordinary skill in the art, with the benefit of this disclosure, will readily be able to determine the type and amount of additive useful for a particular application and desired result.

As previously mentioned, embodiments of the lost circulation compositions may rapidly develop static gel strength. For example, the lost circulation compositions may be characterized by a 10-second static gel strength of at least about 15 lbf/100 ft² at room temperature (e.g., about 78° F.). By way of further example, the lost circulation compositions may be characterized by a 10-minute static gel strength of at least about 25 lbf/100 ft² at room temperature.

In addition to static gel strength, embodiments of the lost circulation compositions should remain pumpable for an extended period of time. A fluid is considered to be in a pumpable fluid state where the fluid has a consistency of less than 70 Bc, as measured using an FANN Atmospheric Consistometer Model 165AT (available from FANN Instrument Company, Houston, Tex.) at room temperature. In an embodiment, the lost circulation composition should remain pumpable for at least about 1 day. Even further, the lost circulation compositions may remain pumpable at elevated temperatures. In another embodiment, the lost circulation compositions may remain pumpable for at least about 1 day at temperature up to about 193° F. In one embodiment, the lost circulation composition has a consistency of less than 35 Bc for at least about 1 day at a temperature up to about 193° F. at 150 rpm. In accordance with present embodiments, when the shear is removed, the composition should gel and, on the other hand, the composition should thin when re-sheared. In one embodiment, the lost circulation composition develops consistency of greater than 70 Bc when the stirring is stopped in a consistometer at room temperature. However, the composition thins to a consistency of less than about 35 Bc when the stirring is resumed at 150 rpm. In addition, the composition should develop gel strength rapidly when left static in certain embodiments. Gel strength development should be followed, for example, by rapid development of compressive strength when left static for longer, time.

As will be appreciated by those of ordinary skill in the art, embodiments of the lost circulation compositions of the present invention may be used to control lost circulation. As previously mentioned, lost circulation zones are often encountered into which drill fluid circulation can be lost. As a result, drilling typically must be terminated with the implementation of remedial procedures, for example. In accordance with embodiments, the lost circulation compositions can be used to seal the lost circulation zones to prevent the uncontrolled flow of fluids into or out of the lost circulation zones, e.g., lost drilling fluid circulation, crossflows, underground blow-outs and the like. In an embodiment, a lost circulation composition is prepared. After preparation, the lost circulation composition is introduced into the lost circulation zone. In an embodiment, the lost circulation composition is pumped through one or more openings at the end of the string of drill pipe. For example, the lost circulation composition can be pumped through the drill bit. Once placed into the lost circulation zone, the lost circulation should set to form a hardened mass inside the lost circulation zone. This hardened mass should seal the zone and control the loss of subsequently pumped drilling fluid, which allows for continued drilling. In addition to drilling fluids, embodiments of the present invention may also be used to control lost circulation problems encountered with other fluids, for example, spacer fluids, completion fluids (e.g., completion brines), fracturing fluids, and cement compositions that may be placed into a well bore.

To facilitate a better understanding of the present technique, the following examples of some specific embodiments are given. In no way should the following examples be read to limit, or to define, the scope of the invention.

COMPARATIVE EXAMPLE

The following series of tests were performed to determine properties of a comparative lost circulation composition. The comparative lost circulation composition had a density of 10 ppg and comprised Class G Portland cement, synthetic clay (Thermavis, available from Halliburton Energy Services, Inc.), and water. Table 1 lists the components and amounts used to design the comparative lost circulation composition. The slurry was observed to be unstable with undesired settling and free water.

TABLE 1 Component Percent of Sample Weight Class G Cement 24.3 Synthetic Clay 0.8 Water 74.9

A static gel strength test was performed on the comparative lost circulation composition using a Fann Model 35 viscometer in accordance with API Recommended Practice 10B-2 (ISO 10426-2). The static gel strength test was conducted at room temperature and 190° F. The static gel strength was recorded at 10 seconds and 10 minutes. The results of the static gel strength tests are set forth in Table 2 below.

TABLE 2 Static Gel Strength (lbf/100 sq ft) Time Room Temperature 190° F. 10 sec 5 9 10 min 7 10

Additionally, the rheological properties of the sample lost circulation composition were also determined using a Farm Model 35 viscometer at the temperature indicated in the table below using a bob and sleeve and spring #1. The results of these tests are provided in the table below.

TABLE 3 Rheological Properties RPM Room Temperature 190° F. 3 3 4 6 4 6 30 5 8 60 7 10 100 9 12 200 10 15 300 14 16 600 25 20

Example 1

The following series of tests were performed to determine properties of a lost circulation composition with a density of 10 ppg that comprised Class G Portland cement, synthetic clay, amorphous silica, a fluid loss control additive, nano-silica, and water. The synthetic clay in the sample was Thermavis with a particle size of 100 microns, available from Halliburton Energy Services, Inc. The amorphous silica in the sample was Silicalite™ cement additive, available from Halliburton Energy Services, Inc. The fluid loss control additive in the sample was HALAD® 344 fluid loss additive, available from Halliburton Energy Services, Inc. The nano-silica was a colloidal nano-silica with a particle size of 5 nm to 8 nm, available as Cemsyn LP from Bee Chems, India. Table 4 lists the components and amounts used to design the lost circulation composition.

TABLE 4 Component Percent of Sample Weight Class G Cement 16.6 Synthetic Clay 0.8 Amorphous Silica 8.3 Fluid Loss Control Additive 0.2 Nano-Silica 2.4 Water 71.6

A static gel strength test was performed on the lost circulation composition using a Fann Model 35 viscometer in accordance with API Recommended Practice 10B-2 (ISO 10426-2), “Recommended Practices for Testing Well Cement.” The static gel strength test was conducted at room temperature and 190° F. The static gel strength was recorded at 10 seconds and 10 minutes. The results of the static gel strength tests are set forth in Table 5 below. As illustrated in the table below, the static gel strength test shows that the sample composition rapidly developed gel strength.

TABLE 5 Static Gel Strength (lbf/100 sq ft) Time Room Temperature 190° F. 10 sec 26 25 10 min 45 140

The rheological properties of the sample lost circulation composition were also determined using a Farm Model 35 viscometer at the temperature indicated in the table below using a bob and sleeve and spring #1. The results of these tests are provided in the table below. The rheology profile in the table below shows a flat rheology profile on shearing at the different rotational speeds.

TABLE 6 Rheological Properties RPM Room Temperature 190° F. 3 16 18 6 22 20 30 50 32 60 51 34 100 52 36 200 54 37 300 55 40 600 56 47

The thickening times of the sample lost circulation composition were then determined using a consistometer in accordance with API RP 10B, “Recommended Practices for Testing Oil-Well Cements and Cement Additives.” The test was performed at 193° F. and a constant pressure of 5,800 psi. The time to test temperature was 18 minutes. The results of this test are shown in FIG. 1. A fluid is considered “non-pumpable” once it exceeds 70 Bc. As illustrated in FIG. 1, the sample lost circulation composition remained pumpable throughout the test with the composition having a viscosity of 30 Bc even after 24 hours at 193° F.

The compressive strengths of the sample lost circulation composition were then determined using an ultrasonic cement analyzer in accordance with API RP 10B, “Recommended Practices for Testing Oil-Well Cements and Cement Additives.” The test was performed at a temperature of 237° F. A first test was performed in which the sample composition was not conditioned. FIG. 2 is a graph of the results of the first test. A second test was performed with the sample composition first conditioned in an atmospheric consistometer for 2:30 hours at 155° F. FIG. 3 is a graph of the results of the second test. As illustrated in FIGS. 2 and 3, the sample lost circulation composition rapidly developed compressive strength upon setting, reaching 50 psi in about 1 hour.

Example 2

The following series of tests were performed to determine properties of a lost circulation composition with a density of 10 ppg that comprised Class G Portland cement, synthetic clay, amorphous silica, a fluid loss control additive, nano-silica, sub micron size-calcium carbonate, and water. The synthetic clay in the sample was Thermavis with a particle size of 100 microns, available from Halliburton Energy Services, Inc. The amorphous silica in the sample was Silicalite™ cement additive, available from Halliburton Energy Services, Inc. The fluid loss control additive in the sample was HALAD® 344 fluid loss additive, available from Halliburton Energy Services, Inc. The nano-silica was a colloidal nano-silica with a particle size of 5 nm to 8 nm, available as Cemsyn LP from Bee Chems, India. The sub micron sized calcium carbonate was a dispersion with a particle size in the range of 200 nm to 800 nm, available from Revertex-KA Latex (India) Pvt. Ltd. Table 7 lists the components and amounts used to design the lost circulation composition.

TABLE 7 Component Percent of Sample Weight Class G Cement 14.0 Synthetic Clay 0.8 Amorphous Silica 8.4 Fluid Loss Control Additive 0.2 Nano-Silica 2.5 Nano-Calcium Carbonate 3.6 Water 70.5

A static gel strength test was performed on the lost circulation composition using a Fann Model 35 viscometer in accordance with API Recommended Practice 10B-2 (ISO 10426-2), “Recommended Practices for testing Well Cement”. The static gel strength test was conducted at room temperature and 190° F. The static gel strength was recorded at 10 seconds and 10 minutes. The results of the static gel strength tests are set forth in Table 8 below. As illustrated in the table below, the static gel strength test shows that the sample composition rapidly developed gel strength.

TABLE 8 Static Gel Strength (lbf/100 sq ft) Time Room Temperature 190° F. 10 sec 21 29 10 min 29 122

The rheological properties of the sample lost circulation composition were also determined using a Fann Model 35 viscometer at the temperature indicated in the table below using a bob and sleeve and spring #1. The results of these tests are provided in the table below. The rheology profile in the table below shows a flat rheology profile on shearing at the different rotational speeds.

TABLE 9 Rheological Properties RPM Room Temperature 190° F. 3 17 25 6 24 27 30 46 45 60 48 46 100 52 47 200 55 48 300 58 51 600 59 55

The thickening times of the sample lost circulation composition were then determined using a consistometer in accordance with API RP 10B, “Recommended Practices for Testing Oil-Well Cements and Cement Additives.” The test was performed at 193° F. and a constant pressure of 5,800 psi. The time to test temperature was 18 minutes. The results of this test are shown in FIG. 4. A fluid is considered “non-pumpable” once it exceeds 70 Bc. As illustrated in FIG. 4, the sample lost circulation composition remained pumpable throughout the test with the composition having a viscosity of less than 50 Bc even after 18 hours at 193° F.

The compressive strengths of the sample lost circulation composition were then determined using an ultrasonic cement analyzer in accordance with API RP 10B, “Recommended Practices for Testing Oil-Well Cements and Cement Additives.” The test was performed at a temperature of 237° F. The results of this test are shown in FIG. 5. As illustrated in FIG. 5, the sample lost circulation composition rapidly developed compressive strength upon setting, reaching 50 psi in about 1 hour.

An on/off test was also performed on the sample lost circulation composition. The test was conducted by placing the sample composition in a HPHT consistometer. The sample was stirred for 2 hours at 150 rpm, allowed to remain static for 15 minutes, and then stirred for 2 hours at 150 rpm. This cycle was performed three times. The test was performed at 193° F. and 5,800 psi. The time to test temperature was 18 minutes. The sample was observed to gel while static but returned to liquid upon application of shear.

For the sake of brevity, only certain ranges are explicitly disclosed herein. However, ranges from any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as, ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. Additionally, whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values even if not explicitly recited. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited.

It should be understood that the compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and steps.

Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Although individual embodiments are discussed, the invention covers all combinations of all those embodiments. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. 

What is claimed is:
 1. A method of servicing a well bore comprising: introducing a lost circulation composition into a lost circulation zone, the lost circulation composition comprising: hydraulic cement in an amount of about 0.1% to about 25% by weight of the lost circulation composition, nano-particles in an amount of about 0.1% to about 10% by weight of the lost circulation composition, amorphous silica in an amount of about 0.1% to about 15% by weight of the lost circulation composition, clay in an amount of about 0.1% to about 2% by weight of the lost circulation composition, and water in an amount of about 60% to about 75% by weight of lost circulation composition; and allowing the lost circulation composition to set in the lost circulation zone, wherein the lost circulation composition seals the lost circulation zone and reduces loss of fluid into the lost circulation zone from subsequently introduced fluids; and preventing loss of fluid into the lost circulation zone from subsequently introduced fluids with the lost circulation composition, wherein the lost circulation composition is shear sensitive, has a 10-second static gel strength of at least about 15 lbf/100 ft² at room temperature, and a 10-minute static gel strength of at least about 25 lbf/100 ft² at room temperature.
 2. The method of claim 1 wherein the lost circulation composition has a consistency of less than 35 Bc at a temperature up to about 193° when under shear at 150 rpm, develops a consistency of greater than 70 Bc when the shear is stopped, and then thins to a consistency of less than 35 BC at a temperature up to about 193° F. when shear is re-applied at 150 rpm.
 3. The method of claim 1 wherein the lost circulation composition has a density of about 6 pounds per gallon to about 14 pounds per gallon.
 4. The method of claim 1 wherein the hydraulic cement is present in an amount of about 10% to about 20% by weight of the lost circulation composition.
 5. The method of claim 1 wherein the hydraulic cement comprises at least one hydraulic cement selected from the group consisting of a Portland cement, a pozzolana cement, a gypsum cement, a high-alumina-content cement, a slag cement, and any combination thereof.
 6. The method of claim 1 wherein the nano-particles comprise at least one nano-particle selected from the group consisting of nano-silica, nano-alumina, nano-zinc oxide, nano-boron, nano-iron oxide, nano-calcium carbonate, nano-clay, and any combination thereof.
 7. The method of claim 1 wherein the nano-particles have a particle size of about 1 nanometer to about 100 nanometers.
 8. The method of claim 1 wherein the nano-particles comprise nano-silica, the nano-silica present in an amount of about 0.5% to about 5% by weight of the lost circulation composition.
 9. The method of claim 8 wherein the nano-silica comprises colloidal nano-silica.
 10. The method of claim 1 wherein the clay comprises a synthetic clay.
 11. The method of claim 1 wherein the clay comprises a synthetic clay, and wherein the nano-particles comprise nano-silica.
 12. The method of claim 1 wherein the lost circulation composition comprises sub-micron sized calcium carbonate.
 13. A method of servicing a well bore comprising: introducing a lost circulation composition into a lost circulation zone, the lost circulation composition comprising: Portland cement in an amount of about 10% to about 20% by weight of the lost circulation composition; nano-silica in an amount of about 0.5% to about 4% by weight of the lost circulation composition, the nano-silica having a particle size of about 1 nanometer to about 100 nanometers; amorphous silica in an amount of about 5% to about 10% by weight of the lost circulation composition; synthetic clay in an amount of about 0.5% to about 2% by weight of the lost circulation composition; and water in an amount of about 60% to about 75% by weight of the lost circulation composition, wherein the lost circulation composition is shear sensitive, has a 10-second static gel strength of at least about 15 lbf/100 ft² at room temperature, and a 10-minute static gel strength of at least about 25 lbf/100 ft² at room temperature; allowing the lost circulation composition to set in the lost circulation zone; and preventing loss of fluid into the lost circulation zone from subsequently introduced fluids with the lost circulation composition.
 14. The method of claim 13 wherein the lost circulation composition has a consistency of less than 35 Bc at a temperature up to about 193° when under shear at 150 rpm, develops a consistency of greater than 70 Bc when the shear is stopped, and then thins to a consistency of less than 35 BC at a temperature up to about 193° F. when shear is re-applied at 150 rpm.
 15. The method of claim 13 wherein the lost circulation composition has a density of about 6 pounds per gallon to about 14 pounds per gallon.
 16. The method of claim 13 wherein the lost circulation composition comprises sub-micron sized calcium carbonate in an amount of about 15% to about 50% by weight of the hydraulic cement.
 17. The method of claim 1 wherein the water is present in an amount of about 50% to about 80% by weight of the lost circulation composition.
 18. The method of claim 13 wherein the lost circulation composition sets to seal the lost circulation zone.
 19. The method of claim 1 wherein the amorphous silica is present in an amount of about 0.1% to about 15% by weight of the lost circulation composition.
 20. The method of claim 13 wherein the lost circulation composition comprises an acid-soluble filler having a particle size in the range of 200 nanometers to 800 nanometers. 